N-terminal truncation contributed to increasing the activity of a novel GH46 family chitosanase

Chitosanase could degrade chitosan efficiently under mild conditions to prepare chitosan oligosaccharides (COSs). COS possesses versatile physiological activities and has wide application prospects in food, pharma-ceutical and cosmetic fields. Herein, a new glycoside hydrolase (GH) family 46 chitosanase (CscC) was cloned from Kitasatospora setae ATCC 33774 and heterologously expressed in Escherichia coli BL21(DE3). CscC has two structural domains, one is the F5_F8_type_C discoidal domain located at the N-terminal, and the other is the catalytic structural domain located at the C-terminal. The truncation of F5_F8_type_C discoidal domain (carbo-hydrate-binding module, CBM) was found to improve the enzymatic properties. Two mutants CscC-CT1 (retaining the linkage) and CscC-CT2 (without the linkage) were obtained. The specific activity of CscC-CT1 was 2.04-fold higher than that of CscC, and CscC-CT2 was almost completely inactivated. The optimum tem-perature and pH of CscC-CT1 were similar to those of CscC (55 degrees C and pH 5.0). In addition, the thermal stability and metal ion stability of CscC-CT1 were better than those of CscC. CscC and its truncation were both determined to be endo-type chitosanases with a polymerization degree of the final product mainly in the range of 1-3. This new chitosanase provides an efficient enzyme tool for clean production of COSs.